Page 241 - DCOM303_DMGT504_OPERATION_RESEARCH

Operations Research

Notes 12.2 Rules in Constructing a Network

1. No single activity can be represented more than once in a network. The length of an arrow
has no significance.
2. The event numbered 1 is the start event and an event with highest number is the end event.
Before an activity can be undertaken, all activities preceding it must be completed. That is,
the activities must follow a logical sequence (or interrelationship) between activities.

3. In assigning numbers to events, there should not be any duplication of event numbers in
a network.
4. Dummy activities must be used only if it is necessary to reduce the complexity of a
network.
5. A network should have only one start event and one end event.
Some conventions of network diagram is shown in Figure 12.10 (a), (b), (c), (d) below:

Figure 12.10 (a), (b), (c), (d): Some Conventions followed
in Making Network Diagrams

(a) Activity B can be performed only
C after completing activity A, and
A B activity C can be performed only
after completing activity B.
B
A (b) Activities B and C can start
simultaneously only after
completing A.
C

A
(c) Activities A and B must be
completed before start of
C activity C.
B

A
C
(d) Activity C must start only after
completing activities A and B. But
activity D can start after
completion of activity B.
D
B

Notes Procedure for Numbering the Events using Fulkerson’s Rule
Step 1: Number the start or initial event as 1.
Step 2: From event 1, strike off all outgoing activities. This would have made one or
more events as initial events (event which do not have incoming activities).
Number that event as 2.
Step 3: Repeat step 2 for event 2, event 3 and till the end event. The end event must have
the highest number.

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